I got 2900 rejected shares in last 2 days, until I restarted the miner. At the moment I'm using cgminer 2.4.3 on win7 64bit with DNS Client service enabled. This is the 2nd time I met this situation. I need to point out that I'm using an internal DNS server (CentOS 5.7, Bind 9.3.6-16.P1) which is configured as both caching and intranet master.